1. Field of the Invention
The present invention is related generally to piston rings and more particularly to intermediate piston rings for disposition between at least two other piston rings in a piston assembly.
2. Related Art
Internal combustion engine manufacturers are encountering increasing demands to improve engine efficiencies and performance, including, but not limited to, improving fuel economy, improving fuel combustion, reducing oil consumption, increasing the exhaust temperature for subsequent use of the heat, increasing compression loads within the cylinder bores, decreasing weight and making engines more compact. In order to satisfy one or more of these demands, many engine manufacturers have been employing advanced technologies to increase the temperature and pressure loads within the combustion chambers of their engines. Consequently, such pistons must be sealed to their respective cylinder bores with piston rings that are designed to withstand the increasingly extreme environment.
Most pistons are sealed against their respective cylinder walls with three piston rings which are axially spaced from one another, and each piston ring is optimized to perform a specific task. Traditionally, the top ring is a compression ring optimized for sealing combustion gasses in the combustion chamber above the piston. The bottom ring is typically an oil control ring which is optimized for scraping the cylinder wall and keeping oil from passing into the combustion chamber. The second, or intermediate, ring typically serves the dual purposes of assisting the top compression ring in sealing the combustion gasses in the combustion chamber and also scraping any oil that made it past the oil control ring.
FIGS. 1 and 2 show a typical intermediate piston ring having a traditional butt joint. As shown, the closed gap between the ring ends of the top compression ring is smaller than the closed gap between the ring ends of the second ring. The purpose of the larger gap in the second ring is to relieve gas pressures between the top and second rings which could otherwise cause the top ring to flutter in the ring groove due to the increased inter-ring pressure. However, this larger total free gap will also reduce the second ring's oil scraping capabilities which could lead to increased oil consumption and also could result in reverse blow-by. There remains a continuing desire for an improved second piston ring capable of preventing flutter of the top ring without compromising the second piston ring's oil scraping and reverse blow-by resistance.